The present invention relates to gas turbine power plant systems wherein the engine is of the variable geometry type. In such systems controls are provided for controlling not only fuel flow but also air or gas flow as well. The air or gas flow is controlled by varying the geometry of the flow path through the engine.
In gas turbine power plant systems, the control of the gas turbine during power-increasing transient intervals has been a problem because of the necessity of avoiding dangerously high turbine inlet temperatures and compressor surge while at the same time increasing the gas turbine speed as rapidly as possible. Heretofore, the problem has been alleviated by providing limiting devices which limit some pertinent engine operating variable either to a specific value or according to a predetermined operating schedule. The disadvantage of a limiting device is that the value to which the selected engine variable is limited depends on such conditions as ambient temperature, pressure, etc., and compensation must be provided for changes in these conditions. Devices capable of accomplishing this compensation are quite complex and expensive.